Liquid electrostatic developers having chargeable toner particles dispersed in an insulating nonpolar liquid are well known in the art and are used to develop latent electrostatic images. Ideally, such liquid developers should be replenishable in the particular equipment in which they are used.
In general, high solids concentration toners are used for replenishment because relatively low concentrations (e.g., in the range of 10 to 15% by weight solids) result in greater liquid build-up in the equipment, which then must be removed and disposed of as hazardous waste. Thus, it is desirable to initially use a toner containing less liquid, and to maintain the working source located within the equipment, thereby minimizing the undesirable accumulation of carrier liquid in the equipment.
When toners are present in the liquid developer in more concentrated form, however, they become difficult to redisperse in the carrier. For example, aggregates may be formed. This can cause serious problems in the replenishment of the liquid developer in the equipment being use.
It has been known to use high shear forces between two closely spaced cylindrical surfaces to dissociate liquid toner particles as disclosed in U.S. Pat. Nos. 5,004,165, 5,048,762, and 5,078,504. These methods have been found acceptable for some applications. However, these dispersion apparatus have the disadvantage in that they require high tolerance, costly mechanical parts to create hydrodynamic sheer and thereby disperse the toner. A need to provide a less expensive and non-mechanical method for dispersing liquid toner still remains.